DBPapers
DOI: 10.5593/sgem2012/s01.v1012

GEOLOGY AND PETROGENESIS OF ORHANELI VOLCANITES, NW ANATOLIA (TURKEY)

S. ALTUNKAYNAK
Wednesday 1 August 2012 by Libadmin2012

References: 12th International Multidisciplinary Scientific GeoConference, www.sgem.org, SGEM2012 Conference Proceedings/ ISSN 1314-2704, June 17-23, 2012, Vol. 1, 99 - 106 pp

ABSTRACT

Miocene volcanic suites are the most common products of post-collisional magmatism
in western Anatolia that is part of the Aegean extensional province. The Orhaneli
volcanic field is situated in NW Anatolia and contains mafic and felsic products of post
collisional volcanism coexisting rhyolite and basalt lavas and associated pyroclastic
rocks. In this region, early pyroclastic products of felsic volcanism were deposited in
lacustrine environment and intercalated with sedimentary rocks. Felsic pyroclastic rocks
are characterized mainly by pumice-ash and ash-block fall deposits and associated
ignimbrites. They interfinger with rhyolitic lava flows at the lower part of the volcanic
sequence. Towards the top of the volcanic sequence basalt lavas are dominant.
Distribution and K/Ar ages of rhyolite and basalt lavas show that they are closely
associated in space and time (19.0-19.4 Ma and 17.5-18.7 Ma, respectively).
Orhaneli volcanites are represented by predominantly High-K calcalkaline series
displaying a gap in silica concentrations. They are significantly enriched in light ion
lithophile elements ( LILE) and light rare earth elements (LREE) but depleted in Zr, Nb
and Ta. These coexisting mafic and felsic lavas have high 87Sr/86Sr values and and low
143Nd/144Nd values suggesting that their magmas derived from lithospheric mantle
source. Basic parental magmas of mafic and intermediate volcanic rocks were generated
from EM1-type mantle previously modified by subduction, whereas felsic volcanic
rocks were produced by assimilation of silicic crust and combined fractional
crystallization (AFC). Major, trace element concentrations, Sr–Nd isotope
compositions combined with regional geology of western Anatolia suggest that the
Early Miocene continental volcanism in NW Anatolia may have been caused by partial
delamination or convective removal of the sub continental lithospheric mantle beneath
western Anatolia.

Keywords: Early Miocene, continental volcanism, Sr-Nd isotope, K/Ar age, Orhaneli
volcanites

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